On and off cycle, i have a 4 pack naturally and I always say I'm gonna do them but I never do, and almost anyone I know with abs doesn't do them. So let's here it, who does the crunches??
There have been studies that have come out that prove crunches don't even stimulate the abdominal muscles enough to provide any benefit. The exercise that tested the highest for rectus abdominis activation was actually the bicycle. Alternating opposite elbow to opposite knee for as many reps as you want seems to work just fine.